Safety assembly for fastener driving tool

ABSTRACT

A safety mechanism particularly suited for smaller fastener driving or applying tools includes a mechanical latch carried on the nosepiece structure of the tool with a part of the latch disposed within the drive track immediately below the end of the driver blade. The latch is coupled to a workpiece engaging member which retracts the latch to permit driver blade movement when the tool is placed adjacent a workpiece. If the tool is operated before being placed against a workpiece, the driver blade engages and locks the latch in latching position so that it cannot be retracted or released by thereafter placing the tool against the workpiece. The illustrated embodiments include both positive and indirect cam type couplings between the latch and the workpiece engaging member as well as pivoting and sliding latches.

United States Patent 91 Wandel et al.

[451 May 7,1974

[ SAFETY ASSEMBLY FOR FASTENER DRIVING TOOL [75] Inventors: Oscar A.Wandel, Mundelein; Frank Mullaney, Villa Park, both of ill.

[73] Assignee: Fastener Corporation, Franklin .Park, Ill.

22 Filed: Feb. 23, 1973 211 Appl. No.: 335,348

3,677,457 7/1972 .Ramspeck Primary Examiner--Granville Y. Custer, Jr.Attorney, Agent, or Firm-Mason, Kolehmainen, Rathburn & Wyss [5 7]ABSTRACT A safety mechanism particularly suited for smaller fastenerdriving or applying tools includes a mechanical latch carried on thenosepiece structure of the tool with a part of the latch disposed withinthe drive track immediately below the end of the driver blade. The latchis coupled to a workpiece engaging member which retracts the latch topermit driver blade movement when the tool is placed adjacent aworkpiece. If the tool is operated before being placed against aworkpiece, the driver blade engages and locks the latch in latchingposition so that it cannot be retracted or released by thereafterplacing the tool against the workpiece. The illustrated embodimentsinclude both positive and indirect cam type couplings between the latchand the workpiece engaging member as well as.

PATENTEDIAY 1 1914 SHEET 2 [IF 2 at W SAFETY ASSEMBLY FOR FASTENERDRIVING TOOL The present invention relates to a fastener driving orapplying tool and, more particularly, to a new and improved safetyassembly for a fastener applying tool.

Safety assemblies for insuring that pneumatic and other power operatedfastener driving or applying tools cannot be operated without beingplaced adjacent a workpiece are well known. Some of these assemblies usea floating fulcrum or other linkage to disable actuation of a singlecontrol valve until the tool is placed adjacent the workpiece and amanual trigger is actuated. Other assemblies use a plurality of controlvalves individually actuated by the manual trigger and the workpieceengaging member.

However, the size of and the space required for these assemblies aresuch that they are not particularly well suited for small tools such asthose driving small or fine wire staples. In addition, these assembliesoperate to restrain operation of the controls for the tools, and it isnot easy to manufacture the same tool both with and without a safetyassembly. This is of particular significance with respect to small toolsbecause at present the requirements for a safety on a small staple ortacker vary considerably. In addition, in instances where this type oftool requires a safety, there is an increasing tendency for the safetyto be such that it requires the tool to be placed against a workpiecebefore the operation of the trigger.

Accordingly, one object of the present invention is to provide a new andimproved fastener applying tool.

Another object is to provide a new and improved safety assemblyparticularly suited for small tools.

A further object is to provide a new and improved safety assemblyrequiring the tool to be placed against the workpiece before operationof the trigger or manual control in order to permit the tool to beactuated.

A further object is to provide a safety assembly that positivelyrestrains driver movement and does not require modification of thestandard controls for the power or drive controlling unit.

Another object is to provide a safety assembly including a latchmechanically movable between blade latching and blade releasedpositions.

ln'accordance with these and many other objects, an embodiment of theinvention comprises a pnuematically actuated tool for applying fastenersor driving staples having a power unit or piston-cylinder arrangementcontrolled by a manual valve for actuating a driver blade which drivesfasteners or staples supplied to a drive track in a nosepiece withinwhich the lower end of the driver blade is reciprocably mounted. Thesafety assembly includes a mechanical latch normally disposed in thedrive track in a position interposed between the lower end of the driverblade and the next staple or fastener to be applied. The mechanicallatch is coupled to a workpiece engaging member projecting below theopening from the drive track through which fasteners are discharged bythe fastener driving blade. When the tool is placed against a workpiecewith the discharging opening in proximity to the workpiece, theworkpiece engaging member is moved and is effective through a couplingto the mechanical latch to retract this latch to a released orineffective position. When the usual manual control such as a trigger isthen actuated to control the power unit to move the driver bladedownwardly, the blade is free to move within the drive track to engageand set a staple.

On the other hand, if the trigger or manual control is actuated beforeplacing the nose piece structure of the tool against a workpiece, thelatch remains in its latching position interposed between the lower endof the driver blade and the fastener to be driven. The force applied tothe blade by the operation of the tool causes the blade to bear againstthe mechanical latch and bias it to a position in which it cannot beretracted. Thus, placing the tool against a workpiece following theactuation of the trigger is not effective to retract the mechanicallatch, and the blade cannot move through its usual power stroke, and thetool can only be operated by releasing the manual control, placing thetool against the workpiece, and thereafter reoperating the manualcontrol.

In the various embodiments of the invention, the latch is mounted forsliding rectilinear or pivoted movement, and the coupling between theworkpiece engaging member and the latch is both positive and indirect.Using the positive coupling, the workpiece engaging member cannot bedepressed if the tool is operated prior to placing the nosepiece againsta workpiece. With the indirect coupling, the workpiece engaging membercan be depressed or actuated following operation of the tool, but hismovement of the workpiece engaging member is not effective to releasethe latch.

Many other objects and advantages of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawings in which:

FIG. 1 is a side elevational view in partial section illustrating afirst embodiment of the safety assembly shown in a latching or normalposition;

FIG. 2 is a fragmentary end elevational view, slightly enlarged, takenin the direction of line 2-2 in FIG. 1;

FIG. 3 is a fragmentary side elevational view, slightly enlarged,showing the safety assembly of FIGS. 1 and 2 in a released position;

FIG. 4 is a fragmentary end elevational view taken along line 4-4 inFIG. 3;

FIG. 5 is a fragmentary side sectional view of a second embodiment ofthe invention shown in a latching position;

FIG. 6 is a fragmentary side elevational view similar to FIG. 5illustrating the safety assembly in an actuated or released position;

FIG. 7 is a fragmentary side sectional view illustrating a thirdembodiment of the safety assembly shown in its normal or latchingposition;

FIG. 8 is a fragmentary end elevational view taken in one direction ofline 8-8 in FIG. 7; and

FIG. 9 is a sectional view similar to FIG. 7 illustrating the safetyassembly in a released or actuated position.

Referring now more specifically to FIG. 1 of the drawings, therein isillustrated a, fastener driving tool indicated generally as 10 having asafety assembly which is indicated generally as 12 and which embodiesthe present invention. The tool 10 includes a housing 14 containing apneumatically actuated piston-cylinder power unit (not shown) forreciprocating a connected driver blade 16, the lower end of which isslidably mounted within a drive track 18 formed in a nosepiece structure20. A magazine assembly indicated generally as 22 disposed between thenosepiece structure 20 and the lower end of a handle portion 14A of thehousing feeds successive fasteners to be applied, such as staples 24from a strip thereof, into the drive track 18.

When the tool 10 is to be operated, the lower end of the nosepiecestructure 20 is placed adjacent a workpiece to actuate the safetyassembly 12. If a manual or trigger actuated control assembly indicatedgenerally as 26 is then operated, the power unit drives the blade 16downwardly within the drive track 18 to engage and set the staple 24supplied to the drive track 18 by the magazine assembly 22. If, on the,other hand, the trigger actuated control assembly 26 is first actuatedprior to placing the nosepiece 20 adjacent a workpiece, the safetyassembly 12 remains in a latch condition, and the driver blade 16 is notfree to move.

The tool can be of any suitable well known construction and, forexample, can comprise a fastener driving tool of the type shown in U.S.Pat. No. 3,673,922. In a tool of this construction, the actuation of thecontrol unit 26 supplies pressurized air to the piston-cylinderarrangement so that the driver blade 16 is driven downwardly through apower stroke. When the control unit 26 is released, the blade 16 isretracted. Alternatively, the control included in the tool 10 could besuch as to automatically restore the blade 16 to its normal positionwhile the control unit 26 remains operated. The magazine assembly 22 canalso be one of those well known in the art and can, for example,comprise the magazine assembly shown in U.S. Pat. No. 3,437,250. Such amagazine includes resilient biasing means for forcing a strip of staples24 to the left (FIG. 1) so that the end staple 24 is always disposedwithin the drive track 18 beneath the lower end of the driver blade 16when this blade is in its normal or retracted position.

The safety assembly 12 is mounted on the workpiece structure adjacentthe front of the tool 10. The assembly 12 includes a mechanical latchmember 28 with a projecting or finger portion 28A. The finger portion28A is interposed between the lower end of the blade 16 and the crown ofthe staple 24 in the drive track 18 when the latch member 28 is in itslatching position. The latch member 28 is provided with access to thedrive track 18 through an opening 30 formed in a front wall 20A of thenosepiece structure. Engagement of the edge surfaces of the latch member28 with the adjacent wall surfaces of the housing 14 and the nosepiecestructure 20 mounts the latch for reciprocating rectilinear movementfrom left to right and from right to left as shown in FIG. 1.

To provide means for controlling the position of the mechanical latch 28in dependence on the position of the tool 10 relative to a workpiece,there is provided a workpiece engaging member or element 32 which isdisposed against the flat outer surface of the front wall 20A within acentrally disposed recess formed in the inner surface of a cover plate34. The plate 34 is secured to the front wall 20A of the nosepiecestructure 20 by any suitable means such as a plurality of machine screwsor bolts 36. The upper end of the retaining plate 34 is provided with acentrally disposed opening in which is received the outer portion of themechanical latch 28 and an outward projection 32A on theworkpiece'engaging member 32. The projection 32A extends generallyparallel to and in a side-by-side relation with the latch member 28.

Toprovide means for shifting the position of the mechanical latch 28 independence on the position of the workpiece engaging member 32, there isprovided a cam follower pin 38 secured to aside wall of the projectingportion 32A on the workpiece engaging member 32. The outer or free endof the cam follower pin 38 is disposed within an upwardly and inwardlyinclined closed slot 40. The slot 40 provides a cam surface, and the pin38 provides a bearing surface bearing against the cam surface defined bythe slot 40. In the normal position of the safety assembly 12 in whichthe latch member 28 is in its latching position with the projectingportion 28A inserted into the drive track 18 beneath the lower end ofthe driver blade 16, the pin 38 occupies the position within the slot 40shown in FIGS. 1 and 2 of the drawings. This normal position isestablished by a compression spring 42 disposed within a centrallyformed slot 44 in the workpiece engaging member 32 and interposedbetween the part of the member 32 defining the lower end of the slot 44and a pin or projection 34A formed integral with or secured to theretaining plate 34 and normally disposed within the upper end of theslot 44. This compression spring 42 biases the workpiece engaging member32 to its lowermost position determined by engagement of the upper endof the slot with the projection 34A. In this position, the lower end ofthe workpiece engaging member 32 projects beyond the lower end of thedrive track 18 and more specifically below a fastener dischargingopening 18A therein.

When the tool 10 is to be operated in its proper sequence, the lower endof the nosepiece structure 20 containing the opening 18A is pressedagainst or immediately adjacent a workpiece 46 including, for example, alayer of material 46A to be attached to a base member 46B. When the toolis moved to this position (FIG. 3), the workpiece engaging member 32 ismoved upwardly against the bias of the compression spring 42 so that thepin 38 moves upwardly within the slot 40. During relative movementbetween the pin 38 and the slot 40, the mechanical latch 28 is displacedto the left from the position shown in FIG. 1 to the position shown inFIG. 3 so that the projecting portion 28A on the latch member 28 iswithdrawn from the drive track 18 to a position disposed to the side oflower end of the driver blade 16. During this movement, the compressionspring 42 is compressed between the material defining the' lower end ofthe slot 44 and the pin or projection 34A on the retaining plate 34(FIG. 4).

If the manual control 26 is then actuated, the power unit moves thedriver blade 16 downwardly so that it engages the crown of the staple 24in the drive track 18 and moves this staple downwardly through thedischarge opening l8A. Further movement of the driver blade 16 drivesthe staple 24 through the parts 46A and 46B of the workpiece 46. Whenthe driver blade 16 is retracted, the magazine assembly 22 feeds thenext staple 24 into the'drive track as soon as the lower end of theblade 16 clears the next staple 24 supplied by the magazine 22. If thetool 10 is maintained in constant engagement with the workpiece, as bysliding the tool 10 along the workpiece 46, the trigger or manualcontrol unit 26 can be reoperated to drive additional staples;

However, when the tool is lifted out of engagement with the workpiece46, the compression spring 42 biases the workpiecev engaging member 32downwardly from the position shown in FIGS. 3 and 4 to the positionshown in FIGS. 1 and 2. During this movement, the bearing surface on thepin 38 slides along the cam surface defined by the slot 40 and shiftsthe mechanical latch 28 to the right from the position shown in FIG. 3to the position shown in FIG. 1 so that the projecting portion 28A onthis latch is interposed between the staple 24 in the drive track 18 andthe lower end of the driver blade 16.

If an attempt is now made to operate the tool 10 by actuating thecontrol unit 26, the driver blade attempts to move downwardly, and itslower end bears against the projecting portion 28A on the latch 28. Thisclamps the mechanical latch 28 against the adjacent surfaces of thehousing 14 and the front wall A of the nosepiece to hold it in positionas well as arresting down ward movement of the driver blade 16. Sincethe lower end of the driver blade 16 is positioned in immediateproximity to the projecting portion 28A, the blade 16 does not attainany appreciable amount of energy, and the mechanical latch 28 is notinjured. In this manner, operation of the tool 10 to drive a staple 24into the workpiece 46 is inhibited whenever the control 26 is operatedprior to placing the nosepiece structure 20 against or adjacent theworkpiece 46.

The pin 38 and the slot 40 in the mechanical latch 28 provide a positivecoupling between the latch 28 and the workpiece engaging member 32.Thus, if the latch 28 is held inits latching position by the biasingforce applied by the lower end of the actuated blade 16, the workpieceengaging member 32 cannot be displaced from the normal position shown inFIGS. 1 and 2. In

other words, with the mechanical latch 28 held in the position shown inFIG. 1 by engagement with the lower end of the blade 16, any attempts toforce the member 32 upwardly by placing the tool against the workpieceare ineffective because the forces that can be developed tending to movethe mechanical latch 28 to the left (FIG. 1) by applying upwardlydirected force to the lower end of the member 32 are not sufficient toovercome the retaining or clamping force applied to the projection 28Aby the driver blade 16. Thus, the tool 10 cannot be made tooperate'after the control 26 has been operated by forcing the workpieceengaging member 32 against the workpiece 46. When the tool 26 isreleased and the pneumatic bias removed from the in-FIG. 3.

Referring now more specifically to FIGS. 5 and 6 of the drawings,therein is illustrated another embodiment of the safety assembly whichis indicated generally as 50. The safety assembly 50 can be used w iththe tool 10 and is'shown in the drawings in conjunction with such atool. However, in FIGS. 5 and 6, the front wall of the nosepiecestructure 20 is designated as 52 rather than as 20A as in theembodiment'shown in FIGS. 1-4 because of slight structural differences.The safety assembly 50 is mountedon the front wall 52A and providesmeans for positively retaining or latching the driver blade 16 in itsnormal or retracted position whenever the tool 10 is operated by theactuation of the control unit 26 prior to placing the dischargingopening 18A adjacent the workpiece 46.

To provide means for normally latching or retaining the driver blade 16in its normal or retracted position, a generally U-shaped mechanicallatch 54 with an L- shaped upper portion is provided. The front wall 52includes a smaller lower opening 56 in which the lower leg of the latch54 is disposed and a larger upper opening 58 communicating with thedrive track through which an upper leg of the latch 54 extends so as tobe disposed beneath the lower end of the driver blade 16 in the normalor latching position of the latch member 54. A compression spring 60disposed in an outwardly facing recess in the front wall 52 engages thebight portion of the U-shaped latch 54 to provide a bias directed to theleft in FIG. 5.

To provide means for shifting the position of the latch 54 in dependenceon placing the tool 10 against a workpiece 46, there is provided anelongated closed wire loop forming a workpiece engaging member 62. Alower bight or transverse portion 62A of the workpiece engaging member62 is normally disposed beneath the discharge opening 18A from the drivetrack in the nosepiece structure 20. A compression spring 64 interposedbetween the housing 14 and an upper transverse or bight portion 628 onthe workpiece engaging member 62 biases the portion 628 into engagementwith the area forming the junction of the leg and bight portions of thelatch 54. The parts of the assembly 50 are retained in position adjacentthe front wall 52 of the nosepiece structure 20 by a generally U-shapedcover plate 66 which is secured to the nosepiece structure 20.

The compression spring 64 is stronger than the compression spring 60,and thus the compression spring 64 acting on the top bight portion 628of the workpiece engaging member 62 overcomes the bias of the spring 60and forces the end of the upper leg of the latch 54 to the normalposition within the drive track 18 disposed beneath the lower end of thedriver blade 16 as shown in FIG. 5. When the tool 10 is moved againstthe workpiece 46 (FIG. 6), the lower bight portion 62A engages theworkpiece 46, and the workpiece engaging member 62 is moved upwardlyagainst the bias of the compression spring 64. The bight portion 623provides a bearing surface bearing against a cam surface provided by thearcuate junction of the leg and bight portions of the latch 54. Thus, asthe bight portion 62B moves upwardly, the compression spring 60 iseffective to pivot or displace the mechanical latch 54 to the left tothe position shown in FIG. 6 so that the outer free end of the upper legof the latch 54 is moved from beneath the lower endof the driver blade16. Thus, when the manual control26 is operated, the driver blade 16 isfree to move downwardly, and drive the staple 24 within the drive track18 into the workpiece 46, as shown in FIG. 6. So long as the tool 10 isheld against the workpiece 46, the manual control 26 can be repeatedlyoperated to produce repeated power strokes of the tool during whichsuccessive staples 24 are driven.

When the tool 10 is moved away from the workpiece and the driver blade16 is retracted to its normal position, the compression spring. 64 movesthe workpiece engaging member 62 downwardly so that the bearing surfaceprovided by the bight portion 628 cams against the arcuate cam surfaceon the latch 54. This cams the upper leg of the latch 54 into the drivetrack 18 so that thereby forces the lower end. of this blade against thefreeend of the upper leg of the mechanical latch 54 and forces thislatch into contact with the cover plate 66 and portions of the frontwall 56 to lock this latch in the latching position shown in FIG. 5. Ifthe tool is thereafter placed against the workpiece 46, the workpieceengaging member 62 can be moved upwardly against the bias of thecompression spring 64 because of the indirect coupling between themember 62 and the mechanical latch 54. However, the biasing forceapplied to the-mechanical latch 54 bythe blade 16 exceeds the resilientbias afiorded by the spring 60, and

the latch 54 remains in its latching position. It is necessary torelease the manual control 26 to remove the driving force of the driverblade 16 before the spring 60 is effective to retract the latch 54 toits released position. Reoperation of the manual control 26 at this timepermits the driver blade to move through a fastener driving stroke. r

A third embodiment of a safety assembly which is indicated generally as70 is illustrated in FIGS. 7-9 of the drawings. The safety assembly 70is also adapted for use with a fastener driving tool similar to thefastener driving tool 10 including 'the power unit for reciprocating thedriver blade 16 and the magazine assembly 22 for supplying successivestaples or fasteners 24 to the drive track 18 in the nosepiece 20. Inthe safety assembly 70 the front wall of the nosepiece structure 20 isof a different configuration from the front walls 20A and 52 of thesafety assemblies 20 and 50, respectively, and the front wall of thenosepiece structure 20 in the safety assembly 70 is designated as 72.

To provide means for preventing movement of the driver blade 16 out ofits normal position whenever the manual control 26 for the tool 10 isoperated prior to placing the discharge opening 18A against theworkpiece 46, a generally L-shaped mechanical latch 74 is providedhaving an upper leg 74A which extends through an opening 76 in the frontwall 72 so that the outer free end of the leg 74- is disposed within thedrive track 18 immediately beneath the lower end of .the driver blade 16and above the crown of the staple 24 supplied to the drive track 18 bythe magazine 22. The lower end of the other leg of the mechanical latch74 is bifurcated or provided with a notch and rests on a locating pin78. One end of the pin 78 is staked or otherwise secured to the frontwall 72. A collar 78A is provided on the pin 78 to aid in locating thelatch 74 and to permit a limited degree of pivotal movement of the latchabout its point of engagement with the pin 78. The outer end'of thelocating pin 78 is received within an opening formed in a closure plate80 which is secured to the front wall 72 by a plurality of suitablefastening means such as machine bolts or screws 82. The front wall ofthe retaining plate or housing 80 is spaced from the grooved surface ofthe front wall 72 to define a cavity for receiving the moving componentsof the safety assembly 70.

To provide means for controllinglmovement of the mechanical latch 74between its latching position (FIG. 7) and its released position (FIG.9), a workpiece engaging member 84 is provided. The workpiece engagingmember 84 includes a somewhat thicker lower end portion 84A, the lowersurface of which is adapted to be placed in engagement with theworkpiece 46. This portion 84A is slidably mounted within a groove orchannel 86 formed in the lower end of the front wall .72 of thenosepiece structure 20. A central portion of the member 84 is providedwith alongitudinally extending opening 88 which at its lower endreceives a compression spring 90, the lower end of which bears againstthe member 84 and the upper'end of which bears against a shoulder 72Aterminating the upper end of the groove 86. The compression spring 90normally biases the workpiece engaging member 84 to the normal positionshown in FIGS. 7 and 8 in which-the lower end of the portion 84Aprojects beyond the'discharge opening within an opening or recess 96 inthe front wall 72 engages the longer leg of the latch 74 andcontinuously biases the bearing surface on the latch 74.against the camsurface 92. The compression spring 90 provides a greater biasing forcethan the spring 94 so thatin the normal position of the assembly (FIGS.7 and 8) the free end of the leg-74A of the latch 74'is disposed beneaththe lower end of the driver blade 16. v

When the tool 10 is moved against the workpiece 46 (FIG. 9), the endportion 84Aof the workpiece engaging member 84 engages the workpiece 46and is moved upwardly against the bias of the spring 90. During thismovement the cam surface 92 moves upwardly, and the flat spring 94pivots the latch 74 in a counterclockwise direction about the pivotdefined by the pin 78 from the position shown in FIG. 7 to the positionshown in FIG. 9. This retracts the leg 74A of the latch 74 from thedrive track 18 andpermits the driver blade 16 to move downwardlythrougha power or fastenerdriving stroke when .the manual control 26 isactuated. The tool 10 can be operated one or more times so long as theworkpiece erigaging member 84 is maintained in engagement with theworkpiece 46 and is held in its upper or actuated position.

When the tool 10 is removed from the workpiece 46, the compressionspring moves the workpiece engaging member 84 downwardly so that the camsurface 92 acting on the bearing surface formed on the latch 74 pivotsthis latch in a clockwise direction from the position shown in FIG. 9 tothe position shown in FIG. 7

- against the bias of the flat spring 94. This moves the leg 74A of thelatch beneath the retracted driver blade 16. Any operation of the manualcontrol 26 and thus of the tool 10 with the' assembly 70 in the positionshown in FIG. 7 moves the driver blade 16 into engagement with the leg74A to prevent downward movement of the blade 16 through a fastenerdriving stroke.

The biasing force applied to the latch leg 74A by the driver blade 16under these conditions is such that the latch 74 is locked in itslatching position. Since the safety assembly 70 includes an indirectcoupling between the workpiece engaging member 84 and the latch 74, theworkpiece engaging member 84 will be elevated to its actuated positionshown in FIG. 9 by placing the operated tool against the workpiece 46.However, the biasing force applied by the blade 16 to the latch leg 74Aexceeds the bias of the flat spring 94, and the mechanical latch 74remains in its latching position even though the workpiece engagingmember 84 is actuated to its elevated position. The tool 10 can beoperated only by releasing the manual control 26 and thereafteroperating this control with the tool 10 in a position against theworkpiece 46.

Although the present invention has been described with reference to anumber of illustrative embodiments thereof, it should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art which will fall within the spirit and scope of theprinciples of this invention.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. In combination with a power driven blade for driving fasteners into aworkpiece,

a drive track structure defining a drive track in which a fastenerengaging portion of the blade is movable and from a lower end portion ofwhich a fastener driven by the blade is discharged,

a mechanical latchmovable into and out of the drive track and normallyin a latching position latching the blade to prevent movement thereof,

a workpiece engaging means movably mounted adjacent the lower endportion of the drive track and movable from a normal position to anactuated position when the drive track structure is disposed adjacent aworkpiece,

and release means coupled between the mechanical latch and the workpieceengaging means for controlling movement of the mechanical latch relativeto the drive track to a released position in which the blade is free tomove through the drive track and discharge a fastener when the workpieceengaging means is moved from its normal position to its actuatedposition. I

2. The combination set forth in claim 1 in which the mechanical latchincludes a blade engaging portion extending transverse to the drivetrack and underlying the fastener engaging portion of the blade in closeproximity thereto when the mechanical latch is in its latching position.

3. The combination set forth in claim 1 in which the release meansincludes resilient means biasing the mechanical latch to its releasedposition and cam means moved by the workpiece engaging means and coupledto the mechanical latch for controlling movement of the mechanicallatch.

4. The combination set forth in claim 3 including additional resilientmeans biasing the cam means to move the cam means to move the latchmeans to its latching position.

5. The combination set forth in claim 1 in which the release meansincludes structure on the workpiece engaging means and the mechanicallatch de' fining sliding cam engagement surfaces for controllingmovement of the latch between its latching and released positions. 6.The combination set forth in claim 5 in which the mechanical latchincludes a cam surface,

and the workpiece engaging means includes a surface bearing on the camsurface on the mechanical latch.

7. The combination set forth in claim 6 in which the cam surface on themechanical latch is defined by an elongated slot,

and the surface bearing on the cam surface includes a pin carried on theworkpiece engaging means and disposed within the slot.

8. The combination set forth in claim 5 in which the workpiece engagingmeans includes a cam surface,

and the mechanical latch includes a surface bearing on the cam surfaceon the workpiece engaging means.

9, The combination set forth in claim 1 in which the workpiece engagingmeans includes a member slidably mounted on the drive track structureand having an opening therein closed at one end by a transverse portion,

the mechanical latch is disposed within said opening,

and the release means includes a cam surface and a bearing surfaceengaging the cam surface, one of the cam and bearing surfaces beingformed on the latch and the other of the cam and bearing surfaces beingformed on said transverse portion of the workpiece engaging means.

10. The combination set forth in claim 9 in which the mechanical latchincludes a generally L-shaped portion with one leg latching the bladeand the junction of the said one leg and the other leg of the generallyL-shaped portion forming one of said surfaces.

11. The combination set forth in claim 1 including means mounting themechanical latch for generally rectilinear movement between its latchingand released positions.

12. The combination set forth in claim 1 including means mounting themechanical latch for generally pivotal movement between its latching andreleased positions.

13. A tool operated by a power unit for applying fasteners to aworkpiece comprising a nosepiece structure defining a drive track intowhich fasteners are fed at a given point and from which fasteners aredischarged through an opening,

a fastener applying element movable by said power unit in said drivetrack between a retracted and an operated position to apply fasteners tothe workpiece through the opening,

a mechanical latch movable between a latching position latching thefastener applying element against movement to its operated position anda released position permitting movement of the fastener applying elementto its operated position,

workpiece engaging means movable from a normal position to an actuatedposition when the opening from the drive track is placed adjacent theworkpiece,

release means coupled between the latch and the workpiece engaging meansfor moving the latch from its latching position to its released positionwhen the workpiece engaging means is moved to its actuated position,

and control means operable to control the power unit to move thefastener applying element toward its operated position, said fastenerapplying element being free to move to its operated position when thelatch is moved to its released position prior to operation of thecontrol means, said fastener applying element applying a biasing forceto the latch to hold it in its latching position when the control meansis operated prior to movement of the latch to its released position.

14. The tool set forth in claim 13 in which the release means includesresilient means applying a given biasing force to the latch biasing thelatch toward its released position and said given biasing force is lessthan the biasing force applied to the latch by the fastener applyingelement.

15. The tool set forth in claim 13 in which the release means includesstructure providing a positive coupling between the latch and theworkpiece engaging means to preventvmovement of the workpiece engagingmeans from its normal position when the latch is held in its latchingposition by the fastener applying element.

16. The tool set forth in claim 13 in which the release means includesstructure providing an indirect coupling between the latch and theworkpiece engaging means to permit movement of the workpiece engagingmeans to its actuated position when the latch is held in its latchingposition by the fastener applying element.

17. The tool set forth in claim 13 in which the latch includes anL-shaped portion with one leg movable into and out of the drive track,

means are provided including the other leg of the L- shaped portion formounting the latch for pivotal movement relative to the nosepiecestructure,

and resilient means are provided acting on the latch for biasing thelatch toward its released position.

18. The tool set forth in claim 17 in which the release means includes acam surface and a bearing surface bearing on the cam surface forcoupling the latch to the workpiece engaging means, one of said surfacesbeing formed on the workpiece engaging means and the other surface beingformed on the latch.

1. In combination with a power driven blade for driving fasteners into aworkpiece, a drive track structure defining a drive track in which afastener engaging portion of the blade is movable and from a lower endportion of which a fastener driven by the blade is discharged, amechanical latch movable into and out of the drive track and normally ina latching position latching the blade to prevent movement thereof, aworkpiece engaging means movably mounted adjacent the lower end portionof the drive track and movable from a normal position to an actuatedposition when the drive track structure is disposed adjacent aworkpiece, and release means coupled between the mechanical latch andthe workpiece engaging means for controlling movement of the mechanicallatch relative to the drive track to a released position in which theblade is free to move through the drive track and discharge a fastenerwhen the workpiece engaging means is moved from its normal position toits actuated position.
 2. The combination set forth in claim 1 in whichthe mechanical latch includes a blade engaging portion extendingtransverse to the drive track and underlying the fastener engagingportion of the blade in close proximity thereto when the mechanicallatch is in its latching position.
 3. The combination set forth in claim1 in which the release means includes resilient means biasing themechanical latch to its released position and cam means moved by theworkpiece engaging means and coupled to the mechanical latch forcontrolling movement of the mechanical latch.
 4. The combination setforth in claim 3 including additional resilient means biasing the cammeans to move the cam means to move the latch means to its latchingposition.
 5. The combination set forth in claim 1 in which the releasemeans includes structure on the workpiece engaging means and themechaniCal latch defining sliding cam engagement surfaces forcontrolling movement of the latch between its latching and releasedpositions.
 6. The combination set forth in claim 5 in which themechanical latch includes a cam surface, and the workpiece engagingmeans includes a surface bearing on the cam surface on the mechanicallatch.
 7. The combination set forth in claim 6 in which the cam surfaceon the mechanical latch is defined by an elongated slot, and the surfacebearing on the cam surface includes a pin carried on the workpieceengaging means and disposed within the slot.
 8. The combination setforth in claim 5 in which the workpiece engaging means includes a camsurface, and the mechanical latch includes a surface bearing on the camsurface on the workpiece engaging means.
 9. The combination set forth inclaim 1 in which the workpiece engaging means includes a member slidablymounted on the drive track structure and having an opening thereinclosed at one end by a transverse portion, the mechanical latch isdisposed within said opening, and the release means includes a camsurface and a bearing surface engaging the cam surface, one of the camand bearing surfaces being formed on the latch and the other of the camand bearing surfaces being formed on said transverse portion of theworkpiece engaging means.
 10. The combination set forth in claim 9 inwhich the mechanical latch includes a generally L-shaped portion withone leg latching the blade and the junction of the said one leg and theother leg of the generally L-shaped portion forming one of saidsurfaces.
 11. The combination set forth in claim 1 including meansmounting the mechanical latch for generally rectilinear movement betweenits latching and released positions.
 12. The combination set forth inclaim 1 including means mounting the mechanical latch for generallypivotal movement between its latching and released positions.
 13. A tooloperated by a power unit for applying fasteners to a workpiececomprising a nosepiece structure defining a drive track into whichfasteners are fed at a given point and from which fasteners aredischarged through an opening, a fastener applying element movable bysaid power unit in said drive track between a retracted and an operatedposition to apply fasteners to the workpiece through the opening, amechanical latch movable between a latching position latching thefastener applying element against movement to its operated position anda released position permitting movement of the fastener applying elementto its operated position, workpiece engaging means movable from a normalposition to an actuated position when the opening from the drive trackis placed adjacent the workpiece, release means coupled between thelatch and the workpiece engaging means for moving the latch from itslatching position to its released position when the workpiece engagingmeans is moved to its actuated position, and control means operable tocontrol the power unit to move the fastener applying element toward itsoperated position, said fastener applying element being free to move toits operated position when the latch is moved to its released positionprior to operation of the control means, said fastener applying elementapplying a biasing force to the latch to hold it in its latchingposition when the control means is operated prior to movement of thelatch to its released position.
 14. The tool set forth in claim 13 inwhich the release means includes resilient means applying a givenbiasing force to the latch biasing the latch toward its releasedposition and said given biasing force is less than the biasing forceapplied to the latch by the fastener applying element.
 15. The tool setforth in claim 13 in which the release means includes structureproviding a positive coupling between the latch and the workpieceengaging means to prevent movement of the workpiece Engaging means fromits normal position when the latch is held in its latching position bythe fastener applying element.
 16. The tool set forth in claim 13 inwhich the release means includes structure providing an indirectcoupling between the latch and the workpiece engaging means to permitmovement of the workpiece engaging means to its actuated position whenthe latch is held in its latching position by the fastener applyingelement.
 17. The tool set forth in claim 13 in which the latch includesan L-shaped portion with one leg movable into and out of the drivetrack, means are provided including the other leg of the L-shapedportion for mounting the latch for pivotal movement relative to thenosepiece structure, and resilient means are provided acting on thelatch for biasing the latch toward its released position.
 18. The toolset forth in claim 17 in which the release means includes a cam surfaceand a bearing surface bearing on the cam surface for coupling the latchto the workpiece engaging means, one of said surfaces being formed onthe workpiece engaging means and the other surface being formed on thelatch.